1. Field of the Invention
The present invention relates generally to the production of bent sheets of glass, and more particularly to a novel adjustable mold for bending such sheets.
2. Description of the Prior Art
Curved or bent sheets of glass are commonly used as glazing closures in automotive vehicles and the like. It is imperative that the glass sheets be bent to precisely defined curvatures determined by the configuration and size of the vehicle openings as well as the overall styling of the vehicle. At the same time, the bent sheets must meet stringent optical requirements. i.e., the viewing area of the closure or window must be free from optical defects that would tend to interfere with clear viewing therethrough Thus, it is necessary that the bending apparatus not only shape the glass sheets to precise curvatures, but also that it do so without adversely affecting their optical quality.
Over the years as automotive styling has evolved, the shapes to which the sheets must be bent have become increasingly complex and difficult to efficiently produce on a mass-production basis. Such curved or bent sheets are now generally produced by a so-called "press bending" technique wherein flat glass sheets are heated to a temperature corresponding substantially to the softening point of the glass. The heated sheets are then pressed or shaped to the desired curvature between male and female mold members having complementary shaping surfaces. The bent sheets are cooled in a controlled manner to either anneal or temper the glass as dictated by their intended end use. Such press bending may suitably be carried out with the sheets oriented vertically, horizontally or obliquely. To achieve a high degree of accuracy in the configuration of the curved sheet while minimizing the application of pressure to the glass surfaces in their viewing area by the press members, the male or convex mold member is generally constructed with a solid or continuous shaping surface which contacts the entire surface of the sheet. Conversely, the cooperating female or concave mold member is constructed with an outline or ring-type shaping surface which engages only the peripheral edge portions of the sheet.
Various materials including wood, metal and refractories have been employed in fabricating the solid or continuous shaping surface of such mold members. Due to a number of factors including deterioration of the material and distortion of the bending surface caused by the repeated heating and cooling of the mold over extended periods of use, none has proven entirely satisfactory. Metal molds are frequently employed and although quite durable, they tend to become distorted in the fluctuating temperature environment and as warping or distortion occurs, it is necessary to frequently rework the mold to restore its surface to the prescribed configuration.
Adjustable surface metal molds were developed in response to the distortion problem. Typically, the shaping surface comprises a continuous, relatively flexible metal plate affixed to a rigid backing plate or structure by a plurality of strategically located adjustable posts or screws. The degree of adjustment tolerable is dependent primarily on the thickness and flexibility of the metal employed. Many of the present day automobile windows are formed to compound curvatures, i.e., sheets bent about mutually perpendicular axes of bending. In order to produce these curvatures it is necessary that the metal sheet be preshaped to the approximate desired curvature since the metal is relatively inelastic and not adapted to being formed to compound curvatures by pure bending. Once the curvature is set, slight modifications can be made to the surface configuration by manipulation of the adjusting screws. However, excessive manipulation will cause creases or ripples to form in the surface of the metal sheet, resulting in an unsuitable shaping surface.
More recently, molds having so-called flexible continuous shaping surfaces have been proposed. As disclosed in U.S. Pat. No. 4,522,641, issued June 11, 1985, one such mold utilizes a shaping element comprising a resilient body having a latticework of flexible metal bands encapsulated therein. The shaping element, in turn, is affixed to a base member by a plurality of adjusting devices located at spaced intervals along the flexible bends. The encapsulating material comprising the resilient body and providing the design surface for the shaping element may be a material such as silicone rubber or other resilient material which is flexible and able to withstand the high temperatures to which it is subjected. The glass-facing surface of the shaping element is covered by a layer of material such as fiberglass cloth to present a smooth resilient surface to the heat-softened sheet. It is disclosed that one or more layers of untreated Fiberfrax.RTM. paper may be disposed between the shaping element and fiberglass cloth to insulate the silicone rubber from the heat and smooth out any irregularities which may appear on the surface of the shaping element.
While such molds represent a distinct improvement over earlier solid male molds, considerable time and labor is associated with the assembly of the individual metal bands to form their latticework. Furthermore, certain limitations exist which may restrict their use under some circumstances. The construction is best suited for molds having a generally rectangular configuration, and it is not readily adaptable to more complex configurations, especially those that are relatively narrow or have adjacent sides that form a rather sharp included angle. Such configurations create regions with very limited adjustability and therefore are not well suited for this construction.